Thymulin is a hormone necessary for T cell maturation that is biologically active only when bound to zinc, suggesting a possible mechanism for the action of zinc on immune function, particularly T-cells. The relationship between zinc status (plasma zinc), thymulin and immunity has not been explored in HIV infection, although low levels of zinc-bound active thymulin and plasma zinc deficiency have been found in HIV seropositive people who abuse drugs, and have been associated with accelerated HIV disease progression. A study to explore the relationship between plasma zinc, zinc-bound active thymulin, and indices of HIV disease progression in an HIV seropositive, drug using population of men and women participating in a cohort study is proposed. Plasma from these participants that has been stored at -80?C will be assessed for zinc-bound active thymulin levels. The relationship of zinc-bound active thymulin with plasma zinc, CD4+ cell count, and CD4+/CD8+ ratio, controlling for viral load and antiretroviral medications, will be examined. The moderating effects of drug abuse on these relationships will be evaluated. [unreadable] [unreadable] [unreadable]